The present invention relates to internal combustion engines and more particularly to mechanisms for stopping the flow of fuel when such engines are to stop.
Small internal combustion engines, such as those used to power lawn and garden equipment, have carburetors that receive fuel from a tank. The fuel is mixed that air in the carburetor and the mixture is supplied to the engine cylinder where it is ignited. During the exhaust stroke of the engine the combustion gases are forced from the cylinder through and through a muffler. The muffler becomes very hot due to the combustion gases.
When an operator desires to stop the engine a switch is closed that shorts the electrical ignition system to ground. This action prevents the spark plug from continuing to fire. However, the engine does not stop revolving immediately, but continues to revolve for several cycles. During this continued movement, the fuel mixture is drawn from the carburetor into the cylinder. Because the spark plug is not being fired, the unburnt fuel mixture is forced from the cylinder into the muffler. The muffler still is very hot causing ignition of the unburnt fuel mixture. This phenomenon is commonly called a backfire. Aside from producing a very loud noise, repeated backfires can destroy the muffler.